Resolved the issue with restarting and new players with MySQL.
Resolved the issue where people could steal items from menu with hotbar keys.
Resolved memory leaks: Player-Settings always created new interfaces whenever something that trigger it happened, but never unloaded them. Now we get the CustomPlayer if it exists, otherwise we create it. Datas are unloaded after the player disconnects.
Settings are saved on shutdown/reload: Settings were never saved on shutdown/reload, now instead we save them.
Added debug feature: Added debug in the config along with some messages regarding MySQL and Commands in order to diagnose and solve future problems.
Menu customization feature: Added that you can now customize the menu at your liking. You can change all settings slots and also can enable and disable them!
Again, big thanks to @Maxetto for helping me on this update. Go give him a follow